35° 



NATURAL SCIENCE. 



Nov., 



very great power of generating heat. Birds, as a class, have more 

 red corpuscles than any other animals. Is the spleen, the other 

 great red corpuscle factory, more developed in birds which have little 

 or no marrow ? These physiological problems are of the greatest 

 interest, and I only wish that I were in possession of facts that would 

 throw light upon them. 



Putting physiology out of sight, I am going now to consider why 

 it is that, among birds of powerful flight, we find differences so great 



Humerus of Pomatorhine Skua (a), Vociferous Sea Eagle (b), and Rhinoceros 

 Hornbill (c). 



in the amount of aeration, and why such a poor flyer as the hornbill, 

 is, in respect of bones, so well equipped for aerial navigation. To 

 put physiology aside, is to assume that if hollow bones are advan- 

 tageous to a bird, Natural Selection can bring it about that they 

 become hollow, and that the bird is able to dispense with the 

 marrow. This would indeed be a bold assumption, did we not 

 know that it is an accomplished fact. The bones are hollow and the 

 processes of life continue. 



